Double-screw jack



April 28, 1925. 1535,72?

AIWJOHNSON DOUBLE SCREW JACK Filed March 9, 1925 \\IIII j M Z I 45/ 0'12 Ja/zrzsan Patented Apr. 28, 1925.

UNITED STATES PATENT ()FFICE.

ALVIN L. JOHNSON, OF SPRINGFIELD, MASSACHUSETTS, ASSIGNO'R OF FORT Y-EIGHT PER TO W. GOULDING WARREN, OF HOLDEN, MASSACHUSETTS, AND FOUR PER GEN '1 T0 ALBERT E. FAY, OF WORCESTER, MASSACHUSETTS.

DOUBLE-SCREW JACK.

Application filed March 9, 1925. 'Serial No. 13,952.

To all whom. it may concern:

Be it known that I, ALvIN L. JOHNSON, a citizen of the United States, residing at Springfield, in the county of Hampden and.

State of Massachusetts, have invented a new and useful Double-Screw Jack, of which the following is a specification.

This invention relates to a jack of the double screw type capable of general use but particularly adapted for. automobiles.

The principal object of the invention is to provide a jack of this type which cannot bind or get into a position from which the parts cannot .be moved.

The invention also involves improvements in the details of construction and combinations of parts that will appear.

Reference is to be had to the accompanying drawings, in which Fig. 1 is a central vertical sectional view of a preferred embodiment of this inven tion;

Fig. 2 is a plan of the same with the cover and certain other parts removed;

Fig. 3 is a sectional view of the same on the line 33 of Fig. 1, and

Fig. 4 is a central vertical sectional view showing the guides.

In the double screw jacks now on the market it is possible to turn the parts into such a position that they will bind and cannot be turned into any other position, without taking the jacks to pieces. Although this does not happen often it spoils further sale of the jack when it does happen.

I provide a case or frame 10 with a suitable base and with a cylindrical opening 11 centrally disposed and arranged vertically down through the frame. This is closed at the bottom by a steel disc 12. This cylindrical passage 11 is provided with a plu rality of longitudinal guides 13 extending from near the bottom to the top of the cy lindrical passage. Within this cylindrical passage I mount a screw 15 which I call the outer screw... This referably is provided with a square threa arranged left handed. It fits in the passage 11 so that it can move up and down therein. Near the bottom this 0 screw is provided with a pin 16 extending across it and projecting at both ends past the guides 13 to prevent the rotation of the screw as it is raisedand lowered in the passage. ,These guides are beveled ofi at the top to provide at all points a passage for the pins and prevent them from ever'coming down in contact with a transverse sur- At the top of the casing it is provided with a circular groove 17'of a height and width sufficient to receive the ends of the pin 16 and allow the screw to turn at that point as thepins then are released from the groove 13, as shown in Fig. 3. On the screw 15 I arrange a nut 18 fitting the screw and obviously adapted to raise it by the turning of the nut on account of the pin and slot construction just described. 'Any means can be employed for turning the nut but I have shown it as provided with an integral gear 19 meshing with a bevel gear 20 on a shaft 21 which can be rotated b a wrench or handle as may be desired. e casing has a cover 22 against which the nut exerts its thrust. I

At one side of the frame and just above one of the guides 13 so as to register with one side of it, I provide a spring pawl 23. This is compressed by a spring 24 normally against an angular surface 25 so that the front surface 26 of the pawl will occupy a radial position flush with one side of one of the guides 13 and so that when the pin 16 comes around against it in a direction contrary to the arrow inFig. 2, as shown in full lines, it will be stopped there in registration with the guide. This locates the screw so that it can be lowered in the easing. When the screw is turned in the *direction of the arrow in Fig. 2, which is the direction in which it rotates to raise the work rest, the pins ratchet by the pawl 23 are both preferably square threaded and left handed. On the top of this screw 28 is a work rest 29 which is positively fixed to the screw so that the screw and work rest cannot rotate relatively to each other. This prevents the rotation of the screw 28 at all times when it is supporting the work.

Now in the operation of the device, the operator taking hold of the work rest 29 raises or lowers the screw 28 by turning it until it gets approximately the right adjustment. Then he moves it under the work 30, as shown in Fig. 1, and turns the shaft 21 in the right direction to raise the screw 15 in the frame. \Vhen the screw 15 reaches such a.- oint that the pin 16 enters the groom 1 this screw 15 will immediately and automatically commence to turn without any change in the direction of rotation or other voluntary movement on the part of the operator. It turns in the direction of the'arrow in Fig. 2 and immediately on'account of the fact that the screw 28 is not free to turn that screw will commence to rise. This position of the parts is shown in Fig. 4.

Starting on the downward motion with the parts in the position shown in Fig. 4, turning the shaft 21 in the opposite direction, the nut 18 will cause the screw 15 to turn with it on account of the thrust of the nut against the cover. If the pin 16 is not nearly around to the pawl when this action starts it would bind and check the jack if it were not for the series of beveled guides. With them the round pin will always start down between two guides or on a beveled surface. Further turning of the shaft 21- in the same direction lets the pin down along one of the slanting surfaces easily into one of the grooves. The abrupt front surface of the groove acts as a stop also. The

jack cannot get stuck so that the handle cannot be turned. If the pin 16 should not go down cne of the guides one end of it will come around into contact with the latch 23 and oositively prevent the further rotation of the screw. The nut continues to rotate and consequently the screws will de scend guided by a guide 13. This brings the work rest down a distance equal to the length of the screw 15. After the work is removed from the jack the screw 28 can be screwed downin so that the whole height of the jack is substantially the same as the height of the casing.

In raising the jack from the bottom the same action takes place with the ratchet pawl shown at the bottom in the circular groove 27. The guides are beveled here for the same purpose.

Although I have illustrated and described only one form of the invention I am aware of the fact that modifications can be made therein by any person skilled in the art without departing from the scope of the invention as expressed in the claims. Therefore, I do not wish to be limited to all the details of construction herein shown and described but what I do claim is:

1. In a double screw jack, the combination with the two screws, one within the other, and means for rotating them, of a vertical casing having a series of vertical guides all around the interior provided with slanting surfaces at the end, said surfaces all slanting in the same direction around the casing, and a pin projecting from the screw and adapted to move along the slanting end surface of any guide and then into the guide to prevent the screw from turning.

2. In a double screw jack, the combination with the two screws, one within the other, and means for rotating them, of a casing having a plurality of vertical guides along the interior nrovided with slanting surfaces at both ends, a pin projecting fronr the screw and adapted to move along the slanting end surface of a guide and then into the guide to prevent the screw from turning, and a spring latch at both ends for positively stopping the rotation of the outer screw and guiding it into one of the guides.

3. In a double screw jack, the combination with the two screws, one within the other, and means for rotating the outer one, of a casing having guides extending along it inside, each provided wit-h a slanting surface at the end,'the casing also having a groove around it at the ends of said guides, a projection on the outer screw adapted to I be received in said groove and to move over one of said slanting surfaces and along the guide, and a latch in the groove for positively stopping the rotation of the outer screw and guiding the projection along one ofv the guides.

4. In a double screw jack, the combination with the two screws one threaded in the other, and means for rotating one of them to raise or lower it, of a casing for support- 105 ing the screws, a plurality of guides for preventing the'rotation of one screw where it is being raised or lowered, said guides having slanting ends to permit of their becoming effective for the purpose specified at all points around the circumference, and a latch for positively stopping the rotation of the screws at one point and starting it to move longitudinally.

In testimony whereof I have hereunto afiixed my signature.

ALVIN L. JOHNSON. 

